In the following we present some of the most important lessons learned. They are classified according to the software development phases of requirement gathering, app design and implementation and the final phase of app testing.

Requirement analysis:

• During requirement analysis talk to the user group and to their carers. The schedules and needs of persons with Down’s syndrome are different as the one of the general public.
• Persons with Down’s syndrome like to please. Whenever you ask them if they like something or not, their answer will most likely be “yes”.
• If you want to ask the person with Down’s syndrome if she prefers one thing or another you need to be prepared with hands-on mock-ups or nearly ready versions of the software. This is due to the fact that most persons with Down’s syndrome have difficulties grasping abstract things.

App design:

• Even wearing glasses, persons with Down’s syndrome might have very poor vision. Hence text has to be adjustable to the text size settings of the device.
• When you design the app flow don’t assume that persons with Down’s syndrome will know where to navigate next. Let the flow of the app do that for them. Highlight fields where the next interaction is needed.
• Use symbols wherever you can. The symbols might be supported by additional text.
• Usually the content of an app needs to be highly personalisable. Hence, there is a lot of configuration, preparation work load which usually the carer has to do. Please make sure it is as easy as possible for the carer to input this data. Using a dedicated app to create the content has proven successful.
• Do not give negative feedback to the person with Down’s syndrome. Always formulate in a positive way. If the user has done something wrong, help him, suggest to repeat the action.
• Be aware that the frustration limit of persons with Down’s syndrome is very low. This means that for example there should be no long loading times (when nothing happens on the screen). If this happens they will lose focus and interest and it will be very hard for the carer to redirect the attention of the person with Down’s syndrome to the task.

App testing:

• Pre-testing: Before testing your app with the target user group (persons with Down’s syndrome), test software first with general population. Testing feedback can be in written form from the test participants.
• Testing: After testing with the general population, then intensely test in a small target user group for a short time. Observe the usage closely. Testing results are derived from the observations and from talking to the test participants or to the carer, who can usually explain what additional support would be needed.
• Piloting: After testing with a small user group, extend the number of participants of the target user group as well as the testing period. It is very important to assign first tasks which have to be completed with the help of the app.