I certainly understand your concerns about moving your son back into a school system where "ugly" influences may be at work. However, there are lots of factors that influence the reputation of a school system, so it's important to find out what you can about the actual school and the teachers your son will have when you transfer. You should meet with the building principal and the director of special education and interview him or her as you would do in a private school. A school system which takes pride in its accomplishments also takes time to meet with prospective parents (even if they are taxpayers and not tuition payers), and you owe it to yourself to give the school a chance to "sell itself" to you and your son. Since you are concerned about the quality of special education services he will receive as well as other factors, you might want to talk with other parents of children with special needs (there may be a special education parent advisory group, or a subgroup of the PTA). By getting as much information as you can about the curriculum, the teachers, the culture, and the safety of a school, you will be making a decision based on facts and not rumors or media portrayals. This way, if you look into private schools, you'll have more information on which to make your decision.
It doesn't seem wise to apply to a private school which doesn't have special services or doesn't know how to deal with your son's special needs, when the public school is obligated by law to meet his needs. On the other hand, if a private school, after reviewing your son's records and meeting him can assure you that they are confident that they can meet his needs, you may decide that the private school option allows you to "purchase" the culture in which you would like to see your son educated. You may have to bring in additional supports (tutors, special education consultants) to ensure that your son's needs get met, so be sure the school will agree to work with outside specialists, if need be.
You can find out information about private schools by checking books that describe schools and their offerings. One such book is called the the Directory for Exceptional Children: A Listing of Educational and Training Facilities 1994-95 edited by Porter Sargent. (This is a bit dated, and there may be a new edition coming out.) This may be a place to start. You may also wish to contact the local office of the Learning Disability Association to get recommendations or advice from other parents of children with learning or attentional problems. Also contact the teacher education program at colleges and universities that serve the Houston area and get the opinion of faculty members who supervise student teachers in or consult to area schools.