The results show that attending the training, “Stop the
pain with Happy-Pingu,” is not only associated with a
reduction in pain but also with an increase in healthrelated
quality of life compared to the WLC. Except for
the changes from T2 to T3 (which can be considered as
the consolidation of the treatment effects), the majority of
effect sizes were in the high range. These positive changes
are apparent not only directly after the end of the intervention
but also at the 3-month follow-up, which supports the
intervention’s long-term effects and its successful transfer to
everyday life. It must be emphasized that during a 5-month
waiting period, no significant changes in the WLC could be
observed. This might be interpreted both as indirect support
of the efficacy of the training and as a sign of the persistence
of abdominal pain. A simple “waiting strategy,” such as “the
pain will vanish” or “this is just a temporary stress period,”
does not lead to improvements over time. On the contrary,
children who were WLC did not change their coping strategies
but continued to report that “lying down” or “sleeping”
were their treatments of choice.