The trouble is, some families have a rosy vision of what they think life in Spain is like;they've heard of better quality life, family values, lovely weather , slower pace of life, cost of living lower etc, but time and time again we've heard how children around the age of 10+ often find it very hard in Spanish schools.Although they "pick up the language" quickly, being fluent enough to cope means extra tuition, and maybe they'll be put back a year in school. The homework will hardly allow for much time for family life, hobbies etc, and the cost of school meals books etc add up. So for some children, leaving their friends, learning another language, coping in a strange school can be utter misery, yet parents are determined to live the dream, at all costs.
At least the OP is financially sound, so perhaps international schools would be better for the older children.
Having qualifications doesn't mean it is easy to find work, either.
It's a huge undertaking to move permanently to Spain, but with 4 children, it sounds like a nightmare;If I were the OP, I'd have a holiday home, and wait till the children have left school before moving to Spain;He and his wife will still be young enough to enjoy it.
Don't forget the tax situation in Spain-will he be any better off?

Thanks to everyone so far who has responded, I certainly seem to have started a lovely debate. I agree with everyone in the respect that this is certainly not going to be a walk in the park and am under no dissolutions that we will not be leaving the UK until everything is in place as I have seen this done so many times before. My Spanish is basic and I have a lot of work to do before next year to pick this up. I will research all the leads that everyone have put down and as per advice look at perhaps funding international school.
I would like to finish my reply by saying that I appreciate everyone's input whether positive or negative, at the end of the day a real picture needs painting and I think anyone who moves believing the grass is greener will more than likely come unstuck.

Almost everybody is worse off tax wise. Especially with a personal allowance soon to be £10,500 for each adult in the UK and then a large slug of income at 20% tax. Having 4 kids will help, though as the tax system is quite family friendly.

I'm with you on that score.

Moving anywhere with 4 children is a logistical challenge, we have done it with 2, so it is double trouble.

I would also like to say, not to burn your bridges as regards any property, your home, in the UK.

Renting out for the time it takes for you to decide if Spain is actually for you, is preferable to selling up and possibly not being able to move back, should the situation arise.

There are all kinds of problems in moving to Spain, and in the case of a large group as yourselves, chances are that someone will not settle.

We have had cases of 'boomerang' families, who have flitted back and forth, for all kinds of reasons, usually financial, but often due to children not adapting to a new Spanish school.

I think it is a task beyond most of us, and could be the best or worst thing you ever do for the family unit.

Tax, and social security payments, if you're going to be legal, is a KILLER!

Be aware - or be illegal.

Spain is a nightmare for tax and social security costs.

International school it is then for the kids, I have various prospectuses so will do the sums in a bit; it breaks my financial heart strings but at the end of the day the kids have to come at the top of the pile.
With the agro kids cause, they had better support me in old age!

Also, i always believe in being legal so everything will be paid where due.

I think the two youngest would slot into a Spanish school, they seem to adapt quite easily, it's the elder two (well, certainly the oldest) that would possibly struggle. Friends of ours moved when their son was 11, they waited until he had finished primary school in UK, they put him in an international school and he has done well, currently in university in Spain. Even in the international school most of his friends were Spanish, he used to spend weekends at their place etc, so his Spanish is perfect. He's done well, but he had been visiting Spain since he was born, both parents had a good level of Spanish and they lived in an all Spanish village, all his friends were Spanish.

as parents we all want to do the best for our children, and it is not easy.

You are wise to consider the schools and look for the best option, but I suggest that you look more to the future.

Your 13 year old (when you move) will have three more years of compulsory education, and then potentially could be in the job market.

The jobs for young people are extremely limited in Spain, youth unemployment figures are horrendous, really bad.

Young people are leaving in droves to work for minimum wage jobs in the likes of the UK.

And after only 3 years of Spanish education would your oldest be able to reach the standard required to compete with a Spanish kid in the job stakes, or be at the level to go into further education?

Sometimes the question of what happens after school should be more of a consideration than what kind of school is best, type query.

School days last for a few years, unlike a stream of deadend jobs due to lack of opportunities, that can last a lifetime.

:-) I wish you the best of luck with all you are planning to do: but don't bank on that.

Good luck with that!

With 4 children, you will be paying around 2,500 euros per month in school fees

Hope you have a good job to go to