Grade 2 and he still can't read the clock on the wall

Realised this weekend that my son reads the time on my phone perfectly but the big clock in our hall means nothing to him. Asked him what time it was and he said 'the small hand is on the 4' and stopped there 🙂 Apparently they did a unit on time last year, but it hasn't stuck. Nani is horrified, she says we all knew by 6. Is it worth sitting with him on this, or does it come on its own once they need it? Any games that worked for yours?