Ok few questions.
where in spain is the big one. Spain is highly dialectually differentiated.
EG, mar o meno (correct) ma´meno (common in murcia) ma´m e(adalucian). Phentic spelling and only a small example of the differences
Northern spain uses different more english pronunciation rather than the traditional spanish pronunciation of letters, sound pairs etc.
Which school?
Eg there is one I know of that doesn´t use "qualified" teachers (ok some unqualified people can beat the socks of qualified people and vis versa) BUT they put children up with english familes that speak little or no spanish. NOT helpful for child that is trying to emerse.
Spanish children without exception start learning English from the age of 2 if in nursery and 5 if they start at "primary" school and there english is without expection very good, they also want to practice it during the summer holidays!
I am saying it is a good or bad idea BUT there are a lot of variables to consider.
With young adults these sort of schools etc work very well but don´t expect all spanish / native speakers it will probably be a mix of europeans. It can be a lot of fun then as spanish can be talked for a lot of the day, then there will be french, german, English later on.
hth