Was that you on the comments section, Xab?? So true, so true......
yes it was me
here's what I said for anyone who doesn't want to click the link again
My children are in state education on the Costa Blanca, not Benidorm - but there are a lot of ex-pats here too. They were 4 & 7 when they started in Spanish School. They weren't put back their first year & have never been held back, either. The older one finishes in the top few every year & the younger one gets good grades too, even though dyslexic. In fact she receives one to one help with this.
My older child (13 now ) chose to move into the Valencian line when she started ESO because there would be less foreigners in the class.
Unfortunately some pepole do come over here with teens & put them into state school. Stupid in my opinion. They have little or no chance of learning the language well enough to graduate at 16. These are the kids who skip school & disrupt classes when they do go in.
My children are truly tri-lingual (counting valenciano), but there are indeed kids we know who have been in the system longer than mine who still don't really speak spanish & get held back. The parents of these kids have never learned spanish, take the kids back to the UK in the hols & sometimes in term time too, watch english tele etc. We don't go back to the UK, I speak spanish & understand valenciano, we have spanish tele - ......................... draw your own conclusions.
so that's what I think about state education
as for 'International'......................
My two were in private International school the first year we were here. I still can't decide whether or not it was a complete waste of money & a year! It did give them a bit of a psychological cushion the first year, but educationally it really was a waste of time & money.
That's not to say all International schools are like that, though from reading on various forums I suspect they are in the majority

A lot of Brits here just don't realise that just because you pay for it, it isn't necessarily better. I'd say the school they were at provided a barely adequate 'english state' education.
Given the choice & an endless supply of money I would love my kids to go to a
truly bilingual school - the only ones I know of are fee-paying & beyond our pocket.
For newly-arrived older kids I reckon you have no choice but International/British- it's just downright cruel to put teens into a school where they don't speak the language & have little chance of learning it quickly enough to graduate. You could be completely ruining a young life. Some kids manage - but they are a very small minority.
It is also true that as parents we need to be involved no matter where our kids go to school, and if they are in Spanish state school it means we need to learn the language too.