I have 2 happy girls at Tormead and a happy son at Lanesborough. Both are academic and nurturing schools, giving pupils the time and space to develop their interests and confidence in their abilities.
I think that some local private schools concentrate on excellence in everything to such an extent that, instead of fostering a "give it a go and see what happens" attitude in their pupils, makes some of them incredibly risk-averse at trying anything that they do not feel they can comfortably "ace".
This is hardly a helpful philosophy to take forward into life beyond school and can produce overly-anxious young adults, who lack the resilience to persist at things they find initially difficult. Search for Tormead, GHS and St Catherine's in Bramley (girls only schools) and Lanesborough to find the most recent Mumsnet threads on them all.
Other preps to consider, depending upon your location, are Ripley Court (mixed), Aldro (boys only from Year 3), Cranmore (mixed), St Hilary's and Rydes Hill (mixed but boys leave after Year 2), Hoebridge (mixed) and Halstead (girls only). Good luck and PM me if you have any specific questions about either Tormead or Lanesborough.