Teachers who take on the topic of time usually hit a wall they didn't expect. A child can repeat It is three o'clock quite happily, then guess wildly the moment you hold up a real clock. The reason is that we're teaching two skills at once without noticing: reading a clock face, and saying it in English. A child who still can't read a clock in Thai will come apart on both at the same time.
Step 1: Check they can read a clock at all (Thai is fine)
Spend the first five minutes checking entirely in Thai. Hold up a clock and ask what time it says. Any child who can't answer in Thai needs the clock skill first. The simplest rule for o'clock is this: look at the hour hand and nothing else. The minute hand always points at 12, and whichever number the hour hand points to is the hour.
Step 2: Lay the English over a skill they already have
Once children can read the face, the English for o'clock is easy, because it needs only the numbers 1 to 12 they already know plus one fixed frame, It is ___ o'clock. Practise with a paper clock whose hands turn. You set the time and they say it, then swap over so a child sets the time for a friend.
Teach the matching question at the same time, What time is it?, because an answer means nothing if nobody ever asks.
Tie it to real life so it sticks for good
Have children write out a timetable for their own day: I wake up at six o'clock. I go to school at seven o'clock. The task drills the times and the everyday verbs together, and children love comparing who gets up earliest. The worksheets you pair with it should run both ways, reading the hands and writing the words, and reading the words and drawing the hands, so you test both directions.