I know that I have been looking for a way to assess my student's learning using their devices. I especially have people ask about Math since most math teachers want to see their students' work and not just a multiple choice answer. Well, take a look at The Answer Pad. It's a free web based assessment site. It does have a companion app called TapIt, but it is only available for the ipad. No worries! Students can also use their web browser and complete the formative or summative assessments that you have created. In fact, you use your paper/pencil questions and students simply put in their answer. There are a variety of answer choices available including coordinate grids. Teachers can also tie each question to a common core standard so you can track if students are mastering a particular standard. For math tests, teachers can allow the use of a calculator that is accessible from the student site or the TapIt app. To begin, you simply sign up for a free account, create your classes, and then add your students or have them join by using a code that you create. Here's a short introductory video to tell you more about it.
I'm a 7th grade Reading teacher and a technology lover. During the 2011-2012 school year we implemented a BYOD initiative. I hope that you will find some helpful information here.