Private lesson are a supplement to playing in band, not a replacement. They are designed to reinforce the concepts taught in band and also focus on instrument specific concepts to advance your student.
If you would like your child to advance on playing skills or get one-on-one tutoring with a professional musician, private lessons are definitely encouraged!
Private lessons will have a positive impact on your child's musicianship. I will be more than happy to help you choose a teacher for your student!