wonkey breastroke kick!!

[benn]

I have an 11 year old male swimmer who has three very good strokes. However his breastroke kick is dreadful. I've never encountered it before, but for some reason his left hip dips when raising his legs and during the propulsive phase of the kick, making his kick and body severly imbalanced.
He doesn't have any posture problems and is equal in muscle proportion. Does anyone have any suggestions?:confused:

[nsswimmer]

that's the same exact problem wit my sister!!!! finally my coach suggested maybe she has scoliosis, so she got checked and it was found she has very very slight scoliosis, but it was enough to make her breaststroke all funky. the referees that usually come to our meets know this (how i don't know) and are more lenient on her than normal when she swims breaststroke cuz they know she can't help the way she kicks.