how do you get your children to tell you what happened at school

[Twiglett]

so far we've had 3 years (not including pre-school) of 'dunno', 'can't remember' and 'forgot'

I don't. When I pick him up (reception aged) I ask if he has had a good day, and he says yes. I something ask what he has done but he invariably can't remember, so I have pretty much stopped asking. I will say things like "did you do pe today" if I know it was a pe day, or "was it mrs xyz today" on mrs xyz's day.
He does however tell me snippets at different times, or tells my mum things.
TBH I don't think I have a right to know (although I want to know) if he doesn't want to tell me.
As long as he seems happy to go and is happy there, then that is enough for me.

Feed him first. Never ask directly after school. Wait for about 2 hours and then ask in a roundabout way, weaving questions into a discussion on another subject. But no direct questions or you will get "I can't remember."

fennel - my dd2 is like your dd3 and just makes it up - does this worry you? - mine is quite convincing sometimes - Is it normal for a nearly 4 year old to be so good at lying? - dd1 is the opposite - she's completely honest about everything

I invite one of their friends to tea and ask them what's happened - they're horribly polite and will tell you anything!

Mine often say it is a secret.

I works the other way too.when i started teaching every Monday they had to write their "news". children would write (inY1) i watched tv/went to McD's/ went on the swings.
When their parents looked at their books at parents evening they would say but that is the weekend we went skydiving/to the moon etc.

I ask mine (7 and 5) when they are getting tucked up in bed what was the best bit and worst bit about their day, and then I tell my best bit and worst bit. It can produce really interesting answers.

I once asked DS (Reception) what he did and his response was
"we sat on the floor all day and year 2 ate our lunch"
Like others I use oblique questions like who did you play with, who fed the fish etc.
I also got the school to put very brief notes of what topics they were covering each week on the notice board
e.g. Numeracy - money
as that allows for a more focussed question that might be a springboard / reminder of what he actually did.
I am far more likely to get a response to
Did you pretend to be in a shop and count some money?
rather than
Did you do some numbers today?