The main difference between PebbleGo and TumbleBooks is that they are priced differently and serve different educational functions. Both products are designed to engage students and are recommended for adoption on a school-wide level as opposed to an individual level.
TumbleBooks has a larger library and supports a greater age range. TumbleBooks offers a school access to a large library that includes not just reading but also math and science. TumbleBooks is priced at $799 per year as of 2015, offering discounts if multiple schools/branches purchase the product.
PebbleGo is more compartmentalized than TumbleBooks. Instead of paying one price to access an entire library, units such as animals, science and biographies are licensed for $395 each.
PebbleGo markets itself as a tool to educate students on research methods, while TumbleBooks engages students with a more generalized curriculum.