ABCya provides free online activities and games to help improve elementary students' reading and math skills. All of the content is accessible online and organized by grade level and topic area. 

Free lesson plans aligned to NGSS, student activity sheets, and integrated animations help students understand chemistry in everyday life. (Recommended by TEA)

AnswerGarden is a minimalistic feedback tool. Use it in the classroom as an educational tool or at work as a creative brainstorming tool.

Ascend Math is personalized online math instruction that provides each student with a unique study path through skill gaps at each level.  Individual study plans are prescriptive, adaptive, and automatically assigned.

Ask A Biologist began in 1997 in the School of Life Sciences as a biology learning resource tool for students, teachers, parents, and life-long learners. (Recommended by TEA)