We did exactly the same, changed dd from a small school (100 ish pupils) to a bigger one (900 or so) and have not had one moment of regret! She started at the beginning of this yr (Australia, so the new starts in Feb) and is excelling!
The old school let her down hugely I believe! She is almost 8 & has a spelling age of 6 and a 1/2, because her spelling mistakes were never corrected (witnessed by me & the fact that mistakes are all over her old school work & there is NO attempt at rectifying them). At this new school, their spellings, at least 4 weeks a term, are the children's individual mistakes.
Her reading level has shot from 7 to 18. Because she was tested! The old school tested her at the beginning of the year & 'forgot' to do the quarterly testing for her!
She lost interest in her work I think. She never really got the encouragement that she needed, so didn't really try! They had a 'good progress' system in her class, where the pupils got a reward for their efforts. Only one child a week could be offered a 'reward' (lucky dip type thing) and her teacher told me that children like my dd wouldn't get a chance as they had to encourage the slower learners, hence, dd always saw someone else being rewarded, but never her. That was pretty sad to see.
She LOVED maths, was slightly above average in her class at the start of yr 1, but dropped a lot because she was never helped/encouraged to try harder. Is now getting back to where she was. Only time will tell if she starts to excel at it again!
Her teacher (at the old school) admitted that she didn't have time for the 'average' students in her class because more than half the class was SN & she couldn't cope/give everyone the attention they deserved. being a small school, the chances were that dd would be in exactly the same class in yr2, as she was in yr1. And I couldn't leave her to lose even more confidence in her work/self.
I worried she would get lost in the bigger school, but she hasn't. She is doing very well!
If you are happy that this is the right choice, your dd will be fine & will do well. I couldn't not do anything, as it will have been dd who suffered in years to come, with an inadequate education!