Saw my oldest DCs off to school in the US, (where the 'system' is far from perfect), and with sinking heart found that they would not be doing much in the way of formal learning until age 6 or 7.
Instead they concentrated on learning how to co-operate reasonably in a group, share writing and art supplies, personal/ self care, respectful classroom behaviour, playing co-operatively, speaking coherently to a group and listening attentively (lots of well-organised show and tell, and story reading by teachers), singing, raising hands to speak, plus letter and number recognition at age 4-5, with a little journal writing, drawing or dictation to the teacher -- I began to see the wisdom to it. They were very well conditioned to be responsible for their own behaviour and able to sit and pay attention by the time they were 6.
Many children I knew, including my own DCs, had learned to read by themselves at around age 4, but there was plenty of social and emotional development to occupy them in school, which was half day until age 6.
My DCs who went right through school in the US did very well. I am so glad I finally relaxed and learned to love the method where I had at first seen only madness.