... just wait until they get to senior school - dd went on ski-ing trip (invited in year 7 - first year, went in year 8 - second year), cost £980 for the week. And she has been invited to go again the year after next (would be, what I call, sixth form, I think it is called year 12).
One good thing the school does is, when my daughter started, they had a voluntary savings fund - parent can pay anything they like (or nothing at all) and this can go towards school trips. If you do not touch the savings account, they give you a top-up bonus each year. My ex-husband asks why I just don't put money into a savings account for her but I would never get round to doing it - would always find something else to spend it on as I never have money left over at the end of the month.
Me and my husband (when he left) also decided to start up a separate savings account for the children (3 of them). He reduced my maintenance payments by £30 a month but pays £60 a month into a separate savings account. This pays for school uniform, school trips, swimming lessons, drum lessons, etc. - any payment that is outside my normal monthly expenditure regarding children and their clubs, etc.
My DD is now in year 10, have been saving £15 a month since she first started (for 2 years) and for the last 2 years (nearly 3 years) have been paying £20 a month. I do not use this for any school trips as they usually give enough notice to pay for the trip and I can use the savings account (i.e. the ski-ing trip) and I like to think of this as another little savings fund for my DD when she leaves school. I have 'bribed' her that I will give her £x for every GCSE she passes and £x+x for every pass that she gets that is higher than expected (i.e. expected to get a C but gets a b, gets the £x+x).
I remember when I was doing my 'O' levels (shows how old I am) and my parents treated me with a lump sum payment for every pass I got. I must say it made me put in that little bit extra effort because I know I was going to be rewarded at the end (not only with my examination results but also monetary - which, when you are 16, is very much appreciated)!!!
I can only say that with children aged 15, 11 (starting high school September - more expenditure) and 6, it only gets worse the older they get.