Mine always said "must try harder" in primary school. Yet I passed my 11 plus and entrance tests for an excellent grammar school easily. Much later I (nearly) completed my OU degree. I always thought I would finish it when I retired, but it's too expensive now. I went on to hold pretty responsible jobs, so I am hoping now I have reached 64 that I could stop trying so hard now!
I think the answer to the original question "What do school reports tell you?" is "Not nearly enough".