小朋友發展遲緩，應該入讀邊類學校？

Hoola

If your current school allows him to become Y1, that means in their eyes, he have the capacity to manage Y1 work. If school is not requesting you to defer. I wouldn't defer.

It may be useful to get rid of tier 1 vs tier 2 mentality. What is Tier 1 to you may be rock bottom to others. Find a school that the child is thriving and a school that aligns with your values, so you will have a happy kid, happy parents and happy life.

It is hard to say whether "IB" is good or not in general, as IB is a framework (esp in PYP years), and every school who runs PYP does it so differently. Some are great, while others are not. Personally, I think a lot boils down to management level. Its wise to find a school with strong management team and good quality teachers, who do not settle for what is easy but settle what is best for the children and school.

Right now, it sound like you do not like your current school. By staying, your dislike of it will just grow. A change in environment may do wonders.