J.W.
Hi T.! I don't know about school start dates since we live in the HEB ISD area, but I think you could google it or just go to the Keller ISD website and find out. HEB has a free email program that I subscribe to that keeps me informed here. Maybe Keller has that too?!
I mostly wanted to get in touch with you hoping we can support each other in our efforts to raise bilingual children. You didn't say if you or your hubbie are native Spanish speakers or if you're just progressive enough to be interested in raising bilingual speakers! Regardless, I commend you. I own a business where I provide Spanish classes for preschoolers & my DD is currently four and we're seeking to raise her bilingually. We hope to enroll her in the Spanish Immersion Program here in HEB ISD when she is school-age. (Neither DH or I are native speakers and ours is not a Spanish-speaking household so we would still qualify for the program.)