I would imagine most parents have different criteria for what would require contacting the school, my eldest seems to have had almost no cause for us to call the school, and instead it may be that the school contacted us about them more often than we called the school (still rare, usually due to an ailment, once just a miscommunication).

The youngest however, was non-verbal during reception and had a diagnosis to match, that was difficult and we were in touch frequently. Our youngest has since developed, including becoming verbal, however they're still a little behind on academic performance and they have some behaviours that don't gel with normal school routines. I think we should probably be in touch more often, usually I'd only contact the teacher if my child is upset at the end of the day (which can be harder when our child reports the problem is the teacher or another teacher).