Why It's Not Worth Paying Peanuts

“If you get one of the best teachers, you will learn in six months what an average teacher will take a year to teach you. If you get one of the worst teachers, that same learning will take you two years. There’s a four-fold difference in the speed of learning created by the most and the least effective teachers. And it’s not class size, it’s not between class grouping, it’s not within class grouping – it’s the quality of the teacher.” - Professor Dylan Wiliam, Deputy Director of the Institute of Education

I'm sure he's right, although my contention would be that, if you have a really bad teacher, you'll never learn however long the experience lasts, because you just give up.

I learned long ago that it pays to choose your specialist help with care. The best graphic designers are at least four times better and quicker than the second best. The best programmers create almost error-free code in no time at all, whereas the worst will never get rid of the bugs. That's why it's always worth paying above the average - in the end you get what you pay for.

- From a blog