I have used https://app.diagrams.net/ from app development to website development with Yr9s . This free app gives the students to flexibility to put their ideas in a story board, site maps, flow charts , as part a good design plan.

Then as part of considerations, the students had to answer the below questions in teams

• What are you trying to solve with this app? What are your goals?
• Who do you want to use your app?
• What is target area for your app?
• For which devices is the app developed for?
• How do you want your UI to look like?
• How interactive will it be? How will the user interact with the application?  Will it involve characters, animation, text-based, dialogues or audio? How do you ensure the user friendliness? e.g. easy to navigate, easy to follow instruction?
• Will your app involve sharing information?
• What information is needed? If you are going to share information, what services will you use to store the information?
• What functionality will your app provide?
• finally get a user feedback on the designed app and do the evaluation/reflections process again and implement the user feedback.