Tex. Fam. Code § 156.101
(a) The court may modify an order that provides for the appointment of a conservator of a child, that provides the terms and conditions of conservatorship, or that provides for the possession of or access to a child if modification would be in the best interest of the child and:
(1) the circumstances of the child, a conservator, or other party affected by the order have materially and substantially changed since the earlier of:
Added by Acts 1995, 74th Leg., ch. 20, Sec. 1, eff. April 20, 1995.
Amended by Acts 1995, 74th Leg., ch. 751, Sec. 47, eff. Sept. 1, 1995;
Acts 1999, 76th Leg., ch. 1390, Sec. 16, eff. Sept. 1, 1999;
Acts 2001, 77th Leg., ch. 1289, Sec. 5, eff. Sept. 1, 2001;
Acts 2003, 78th Leg., ch. 1036, Sec. 19, eff. Sept. 1, 2003.
Acts 2009, 81st Leg., R.S., Ch. 727 (S.B. 279), Sec. 3, eff. September 1, 2009.
Acts 2009, 81st Leg., R.S., Ch. 1113 (H.B. 1012), Sec. 28, eff. September 1, 2009.
Acts 2009, 81st Leg., R.S., Ch. 1118 (H.B. 1151), Sec. 3, eff. September 1, 2009.