Teaching 4 basic future forms:

going to vs.
the present progressive vs.
will vs.
the present simple

This deserves a guide to itself because of the deep confusion that arises when people teach the area without thinking things through.

If you are at all unsure about the three main uses of going to, the three main uses of will and the way the present progressive and simple forms are used to talk about the future, you should go to the guide to four future forms and work through that before you do this bit.

Overlapping uses

The first issue in this area is that, although it is temptingly simple to separate the uses of the three types of future, real life, as always, is more complicated than it seems. Here are some examples of the uses of the three forms. Separate them by function and then click here.

I'll be at the meeting this afternoon at 4.
We're having a meeting at 4.
I'm going to come to the meeting at 4.
I'm going fishing alone tomorrow.
I'll have my phone with me if you need anything.
He's going to be delighted with the result.
He'll be delighted with the result.
She's having a birthday party in June.
She's having a baby in June.

Comments:

I'll be at the meeting this afternoon at 4.
This is clearly an expression of willingness and a promise to fulfil an arrangement rather than anything else. It's not a prediction in the accepted use of the term but we have to use will/shall in this case because we have a stative use of the verb be.
For an arrangement like this with a dynamically used verb, we would normally select the present progressive:
I'm presenting the report at the meeting
for example.
However, it is unlikely to cause a communication problem or sound odd if we choose to say
I'm going to present the report at the meeting
is it?
All three of these forms can all be used to talk about arrangements quite naturally because arrangements are premised on people's current willingness and ability.
We're having a meeting at 4.
This is a example of what is usually called the arranged future with the present progressive. However, here there is one oddity: the verb have is being used dynamically (to mean something like hold) so we can use the progressive form. If you try to make the meeting the subject, the problem reveals itself:
    *There is being a meeting at 4
    *The meeting is being at 4
The passive is also a problem: we can have:
    The meeting is being held at 4
but not
    *The meeting is being had at 4
Normally, in fact, we select the simple present to do this:
    The meeting is at 4
It is also possible to have:
    There'll be a meeting at 4
    We'll have a meeting at 4
especially if the information about the arrangement is new to the hearer and there is a clear prediction.
All three forms can be used to talk about arrangements but a 4th form, the present simple, is preferred with the verb be, and can, in fact, be used for many arrangements, especially formal ones:
    This meeting is / takes place at 4 / in Room 3 / with her in the chair
etc. This is not quite the same as a timetabled event because it is not a repeated circumstance. It could be a one-off event.
We can use all 4 forms to talk about arranged events.
I'm going to come to the meeting at 4.
Traditionally, the going to formulation is explained as being used for current intentions. It may have that flavour here but it needn't. This form is also used to talk about arranged events and actions. If the speaker had said:
    I'll come to the meeting at 4
the meaning might show willingness (or a spontaneous decision).
We can also use the going to and will structures to talk about timetables, incidentally:
    The train's going to arrive on Platform 6 at 4:15
    The train will arrive on Platform 6 at 4:15
Those are both predictions based on the present timetable.
I'm going fishing alone tomorrow.
This is the use of the present progressive to talk about the future but it is probably not an arranged event because of the word alone. The issue here is twofold:
1. The use of the present progressive for intentions is often preferred with the verb go to avoid the clumsy going to go fishing formulation.
2. We can use the present progressive to talk about present intentions rather than arrangements because it's not always clear what level of arrangement is meant and how firmly fixed it is. For example,
  I'm taking a holiday in Spain where I'm going to use a hire car to get around
  In that sentence we cannot be sure one way or the other whether the hire car has actually been booked. It may be an arrangement or it may be a current intention.
I'll have my phone with me if you need anything.
You may be tempted to see this as the conventional use of will/shall to express a condition, but it isn't, actually. The sentence means something like
    I'll have my phone with me so call me in the event that you need anything.
The form here is used to show willingness to be contacted.
It is often hard to distinguish between will/shall to express willingness:
    I'll help you do this
and the form of going to to mean something very similar:
    I'm going to help you do this
He's going to be delighted with the result.
He'll be delighted with the result.
It's almost impossible to distinguish a difference in meaning between 6. and 7.
Both are clearly predictions and both are based on some knowledge of the nature of the result and some knowledge of the person in question.
Both going to and will/shall can be used for predictions based on experience.
She's having a birthday party in June.
She's having a baby in June.
8. is probably a current arrangement of some sort (although it could only be her intention and no invitations have been sent).
9., however, is not an arrangement in any accepted sense and we could use the predictive future with will to express the same idea.
We could also say
She's going to have a baby in June
although that clearly has nothing to do with intentionality because it is a prediction.

You can visualise the overlap something like this:

overlapping diagram

(For more on the times when the progressive form of the present and the going to structure are not interchangeable, see the guide to talking about the present. The discussion appears there because both forms are present tenses relating to future events or states.)

This is not an easy area to understand, is it?
It can be unravelled slightly by considering two sorts of futures rather than a lot of conflicting and overlapping forms.

The future as an external event

When we say something like
    The temperature will drop to zero tonight
    The train arrives at 6
    They are staying for a week
    It's going to rain
etc.
we are referring to things outside our current control. They are extrinsic to us. For futures of these sorts, the form we choose depends on the nature of the event.
If we are talking about a simple fact, we'll select will or the present simple:
    It will be wet on the road because it's been raining.
    The plane arrives at 7
etc.
If we are talking about a prediction based on current or past evidence, we'll often select the going to form:
    I've seen the forecast and the weather's going to turn nasty
    He's going to win because he's the fastest
etc.
If we are talking about something fixed and arranged, we'll often select the progressive form:
    He's studying Latin next year at Oxford
    She's taking the train because her car's in the garage
etc.

The future as we see it

This is a form of modality because it concerns how the speaker perceives an event. This is where the going to future is common because it concerns intrinsic matters. For example:
    I'm spending my holiday in Scotland where I'm renting a cottage
these are my current plans for the future
    While I'm there, I'm going to take lots of long walks and I'm going to try to work on my novel
the events are not arranged because they exist only in my head at the moment
    When I finish school, I'm going to university
my place is assured now
    When I grow up, I'm going to be a train driver
nothing is fixed and arranged but this is what's in my head right now
In all these cases the future is seen through the lens of the present. This goes a long way to explaining why present forms are selected.

The generally accepted use of the will/shall future to show willingness (or spontaneous decision) also falls into intrinsic meaning because it refers to my perception of the future and my current mood concerning willingness to do something now or in the future. For example
I'll come early to help you get ready
is not a determined future of any sort. At this stage, it's a current offer. If you accept, it may well become a fixed future and we'll say
I'm coming early to help you get ready, aren't I?

Summary of types of meaning

It looks like this:

summary extrinsic intrinsic

Teaching the forms and uses

Diaries

Just about the most popular way of trying to make the concepts of these two future forms clear to learners is to use some form of diary. Usually, this is set up in such a way that learners have different diary plans and have to negotiate a good time to meet using language such as
I'm sorry, no, I'm watching the football tomorrow night. What about Thursday?
and replying with
Oh, I'm sorry, I'm visiting my mother then
etc.
If you don't believe this is popular, try putting "present continuous for the future using diaries" into an internet search engine and see some of the thousands of hits it records.
So what's the problem?
It doesn't work, that's the problem.

This is because the writers of such exercises have usually lost sight of the fact that diaries used in this way (to project forward) are not actually diaries at all – they are planners. And the problem with plans is that they cover things I am doing and things I am going to do. In other words, we use planners for both intrinsic futures and extrinsic ones. The difference can never be made clear this way.

Say, for example, you have a diary entry for Saturday afternoon which states:
VISIT MUM
Now, you might have written that because you have arranged with your mother to visit or because it is your intention to visit her but no arrangement has yet been made firm. It may even be the case that you are going to drop in unannounced. Who can tell?
So the 'correct' response for Saturday afternoon could be:

I'm visiting my mum on Saturday afternoon
I've arranged this
I'm going to visit my mum on Saturday afternoon
I intend to do this and may or may not have arranged it
I'll visit my mum on Saturday afternoon
I have had the intention for some time and I'm only now telling you about it

If you are trying to use the diary to focus on 1. or 2., you will find yourself in the position of rejecting the other responses. But they are just as 'right'.

Moral: don't use diaries. They confuse more than they enlighten.

This is not confined to the use of diaries (although that's very common).
The problem with many course materials is that they focus on the time and the event not on the internal processes in speakers.

A better idea

The concept to make clear to learners is:
Is this an event that which is a real fact about the future or does it only exist in my head at the moment?

Here's one way to make it clear:

	SITUATION NOW: I feel ill	The present situation is the foundation for all future acts. You need to set the context and the person's current feelings.
	THINK AND DECIDE: I’m going to see the doctor	This is an intrinsic current event. It goes on inside his head.
	ACT NOW: I’ll call to make an appointment (for you)	will/shall as a modal to show willingness (not futurity) or to signal a decision made now
	FIX THE FUTURE: I’m seeing the doctor at noon. I see the doctor at noon.	Two possible tenses to express currently arranged timetables and events. The first is more common for mutual agreements. The second is more common for external events (like trains)
	DECIDE AGAIN: He told me to take some time off so I'm going to talk to my boss. I'll talk to my boss.	going to is often used as a way of saying how you react to something now will/shall implies an immediate, unconsidered, action: a promise to yourself
	ARRANGE: I’m taking a few days off work and ... DECIDE: ... I'm going to stay in bed.	the first is an arrangement the second is intention against the background of the arrangement this is a common way of combining the tense uses

Here's a similar idea with a different focus:

	SITUATION NOW: I'm exhausted.	The present situation is the foundation for all future acts. You need to set the context and the person's current feelings.
	THINK AND DECIDE: I’m going to book a holiday	This is an intrinsic current event. It goes on inside my head now.
	THE FUTURE IS ARRANGED: I'm taking a holiday in Scotland and I'm staying in a hotel by a lake.	We are talking about something which is booked. It is now an external fact, not an internal intention.
	THE FUTURE IS IMAGINED: I'm going to do lots of walking. I'm going to read a lot. I'm going to do nothing at all.	These are not arrangements. They exist only in the current internal world.

Introducing the forms

The ideas above focus on contrasting the forms and that makes good sense because, when we are talking about the future, what will happen and what we are going to do about it occur naturally together. In natural communication, therefore, we might get something like:

A: On the TV, they said it'll be wet and windy tomorrow, you know.
B: Well, if it is, I won't play golf.
A: Golf? I thought you were taking the kids to the park tomorrow.
B: No, I'm taking them on Monday. That's what we talked about yesterday.
A: We did? OK but what are you going to do, then?
B: I don't know. I guess I'll take the kids to the cinema. I'll phone the guys and tell them I won't be free till Monday for the golf.

In that short exchange, we have three future forms being used in different ways to express different ideas. It sounds reasonably natural because the topic stays firmly on the future seen in different ways.
The problem, of course, is to introduce the forms rather than contrast them, especially for lower-level learners.

Keep it focused

At the beginning, try not to have a context where more than one form is possible. For example, don't mix planning and intentionality. It's fine to use planning a trip and booking things to set the idea of the present progressive but if you mix in intentionality people will either get confused or use the wrong form for their meaning.
If you have something like a focus on the idea of booking something, the concept of present progressive for the future becomes clearer.
For example, planning a holiday or a journey requires things to be booked in advance and once that’s done, we can naturally use the tense form for arrangements. E.g.
We are holidaying in the Scottish Highlands, staying in a cottage and spending our time walking and fishing
etc. The idea to get across is one of extrinsic meaning. These things refer to a fixed future, not to someone's view of it.
It is fatal, however, to mix in speculation about what will happen once you get there, because that will usually involve going to as in
When we get to the cottage, the first thing I'm going to do is find out where the nearest pub is.
That is what happens when you try to use diaries for the contrast.

The going to form should be carefully split between the use for prediction based on evidence / experience and use for intentions. The first is extrinsic, the second is intrinsic.

For the prediction use, images are good because we can actually see the evidence:

	She's going to have a baby
	It's going to rain
	Is he going to buy the book? Is he going to steal the book? Is he going to read the book in the shop?
	No. 3's going to win
	She's going to step into the road

For the intention use, you need to set the context of what the situation is now and then people's intentions based on the present become clear.

	I'm thirsty so ...	I'm going to get a drink
	I'm hungry so ...
	She's tired so ...
	Her back aches so ...

The idea of volition is central. In all of these, it's possible to use want to instead of going to so it's a short step to the idea.
Teaching the verb intend is quite a useful thing to do in this context. Then you can say how it differs from arrange.

The present simple is easily presented using timetables but they don't have to be transport timetables. School timetables work well, too, and are often a bit more interesting and familiar, especially to younger learners.

will/shall for willingness can also be set in a present context of situation > problem > offer / suggestion
    Situation: People planning a dinner party.
    Problem: There's no beer in the fridge!
    Solution: Don't worry, I'll get some on my way home.

will/shall for prediction can often be effectively taught within the conditional but it doesn't have to be. We can extend the little dinner-party problem to
    But it won't be cold.
    Yes it will, I'll get it from the place with a fridge.
    It doesn't matter, anyway, because we'll have two hours to let it cool before they come.

Using these ideas

Keeping the context very tight and being very controlled will help you get the various concepts and uses of the forms across but remember that it is only possible fully to grasp the ideas when used in contrast to other forms and uses. Sooner, rather than later, you will have to present and practise the forms together.

There's no rule. Use them as you will, or not.
A simple approach is to take one scenario and present it, practising the language as you go along, and then get the learners to reconstruct the things said and the reasons for the use of each form with a second set of picture prompts.
It is critical that:

You have a clear, memorable context and that's where the picture prompts come in.
You have a way or ways to alert your learners to whether the future is an internally imagined one or an external reality.

If you have taught successful lessons introducing or contrasting the various futures, why not send the ideas to ELT Concourse?

Related guides
four future forms	for the overview of the basic forms and meanings
four more future forms	for an analysis of the less frequent and more complex forms
tense and aspect	for a link to four guides to analysing tense and aspect beginning with a consideration of meaning