Web Application: A Professional Education/Learning System

I need to build a Duolingo or Grovo-like platform for a web based learning system dedicated to primary school kids. In the first stage, the learning system will include exercises for Maths and English. But more modules will be added in the future (i.e. Science, History, Geography, etc...).?What I need right now is an empty but fully functional system with a nice and eye-catchy website design (i.e. [login to view URL]). As for the contents, I want to be able to upload them in any moment later using an intuitive back end system.?This is the kind of content I'd like to insert into the platform: - Maths exercises need to be generated automatically by the system and will have a very similar style as in [login to view URL] - exercises, to be done in many different ways (multiple choices, decision making scenario choices, interactive videos...) - BiteSize learning objects - games The platform should be scalable, with a responsive design that can run on smartphones and tablets, too. The system needs to keep records of all the activities and exercises practiced by each user, and it also has to include a notification system, a tutoring system and it has to allow a user to interrupt his learning path at any point and continue it later without restarting it from the beginning. Users should be able to create an account and pay a month/yearly membership. Further details can be provided later after choosing who is going to work on this project. Please note that this project is for a professional web application NOT just a standard website. So, please only give your offer if you have a good experience working with web applications. People who are going to work on this project, they need to show a very high level of expertise in the following: - javascript - jquery - php - back end programming - database driven web applications - front-end design - front-end development - html5 - user experience design - user interface design - user interface programming - web application design When bidding for this project, please: - give your estimated turn-around-time to accomplish the task. - give an estimate quotation for such project. - include any previous web applications you've made before. PS: we will not consideration any offer from candidates who fail to show the level of expertise and quality needed for this project.