This is an official Houghton Mifflin site-lots of stuff. Click the Students tab and choose a subject area- Reading, math, science, social studies, or spelling. Choose a book (e-books are best), a grade, and it will link you to a variety of activities. I clicked social studies, the social studies e-book, US History, and Interactive Maps. Clicking on the legend adds features to the maps! There are also questions for the students below. In the math category, there are online, interactive games available. In science, there are simulations. Lots and lots of material here.