It's possible your school has web filters in place that restrict access on your computer or your students' computers. Provide your school's technology department with the following urls and they can "whitelist" GrammarFlip and resolve the issue for you:
https://grammarflip-api-user-prod.azurewebsites.net
https://grammarflip-api-admin-prod.azurewebsites.net
https://grammarflip-api-curriculum-prod.azurewebsites.net
https://grammarflip-api-student-prod.azurewebsites.net
https://grammarflip-api-teacher-prod.azurewebsites.net
https://app.grammarflip.com
https://api-user.grammarflip.com
https://api-admin.grammarflip.com
https://api-student.grammarflip.com
https://api-teacher.grammarflip.com
https://api-curriculum.grammarflip.com
fast.wistia.net
embedwistia-a.akamaihd.net
In addition, make sure your school district’s IT department allows access to Slideshare and Wistia. GrammarFlip’s videos and slideshows are hosted on these sites, and it will be important that students have access to these resources. Remember that a teacher’s computer may have the ability to access sites that a student’s computer may not, so be sure to check ahead with your IT department before purchasing. You will want to ask your district to please allow access to these sites and the following urls: