When we first arrived in Spain 2 and a half years ago, i felt the same as you, and wanted my son to go to an English speaking school. But there weren’t any within a reasonable distance.
He has been in the local village school, the only English child, and he now speaks fluent Catalan and Castellano. My friends and family are amazed when they visit, my parents were actually in tears. There are only 9 pupils in his class, and only 67 in the whole school with 8 teachers…........and i dont have to pay a penny.
Yes, his English reading and writing are a little behind what they would be if we were still in the UK, but what the hell, he is tri-lingual at 8 years old, and we are doing lots of practise at home (i have a TEFL qualification)
I wouldn’t be too determined about an English school if i were you, let them integrate into Spanish life and education, it’s a fantastic future for them.