 Houghton Mifflin Harcourt NASDAQ:HMHC was upgraded by Zacks Investment Research from a sell rating to a hold rating in a research report issued on Tuesday, Zacks.com reports. According to Zacks, Houghton Mifflin Harcourt Company is a global provider of education solutions, delivering content, technology, services and media to students in over 150 countries worldwide. The ... 