Trial design {8}
This trial employs a superiority, three-arm parallel-group randomized controlled design, comparing two app-based interventions to a waiting list control condition. Participants will be allocated randomly (in a 1:1:1 ratio) to receive the full-RNT focused intervention via mobile phone app or the concreteness training intervention via mobile phone app or to wait for 18 weeks before being offered one of the two app versions. Thus, the three trial arms are as follows: (1) the full RNT-focused intervention, (2) the concreteness training intervention, and (3) the waiting list control condition.