Kneeling posture

Mrs. Gokhale, Thanks for writing this book - I've been waiting for it for years.  First, while kneeling, should one tighten the inner corset, and tilt the pelvis forward, or some other technique?  (I've had lower back discomfort while kneeling for several years now.)  (I kneel a lot in church.) Extra - I have an eleven year old son who has started slumping so he and I are going through your book together, and he is gradually increasing the exercises you list in the back.  Thanks for all the great photos of persons of all ages in your book.  Also, I impressed my Physical Therapist (went for hip pain, weak core muscles) with my arch muscles in my feet.  He said he had never seen anything like that before.  I wished he would've read your book.  He did glance through it and said, "That's what we want all of our patients to do." Again, thanks so much for your book and I also would buy a yoga DVD of yours. Thanks so much for setting up the forum and for taking the time to consider my questions. Lemontree