How do you teach present continuous tense in a class?

Teach the form and the function.

Form = be verb + present participle. The be verb used depends on the subject:

am for I, is for he/she/it and are for we, they, you.

The functions of present continuous:

1.To talk about an activity that is happening now.

· He is watching TV.

· I am teaching you.

2. To talk about an activity that is happening around now, but maybe not happening right now.

· I am reading a good book.

· He is learning to play the guitar.

3.To talk about a temporary activity.

· We are feeding his cat while he is away.

4. To talk about a planned future arrangement.

· I'm having lunch with Xia tomorrow.

· We are meeting at 6:00pm.

Also you should teach about the spelling variations of present participles

Spelling of verb + ing.

1. Usually add -ing to base form of the verb.

go + -ing → going, wear + -ing → wearing, eat + -ing → eating.

2. Verbs that end in one -e, drop the e.

smoke → smoking, hope → hoping, come → coming, write → writing.

Verbs that end in -ee don't drop an e.

agree → agreeing, see → seeing.

3. Verbs of one syllable with one vowel and one consonant, the consonant is doubled.

stop → stopping, run → running, get → getting.

If the final consonant is -y or -w it is not doubled.

Play → playing, show → showing.

And then there are questions, form and function.