There are a wide variety of primary schools in the UK ranging from large academies catering for in excess of a thousand pupils to small rural primaries which have just two classes and a total of less than fifty pupils on roll. It is a matter of personal choice which setting suits you as a primary school teacher with some teachers starting out at one end of the spectrum and changing their preference as they progress with their career but does it make a difference to your career progression and is a larger school better to work in if you have set your sights on a headship?
The most obvious variance is that a larger school will usually have a higher turnover of staff giving the current staff the opportunity to apply for other roles in the school. On the other hand, it is easier in a smaller setting to take on extra curriculum responsibilities giving teachers the chance to develop their leadership skills in a less threatening environment.
The budget for CPD, that is continuing professional development, in a small school may be insufficient to allow staff to undergo a wide range of training each year thus restricting the opportunity to access the qualifications needed to enable career progression. This should not hold back an ambitious teacher however and promotion prospects should be explored at the annual professional review that each teacher is entitled to.