The field of cognitive training (CT) has been researched for over a century. However, there is still a debate regarding its ability to produce cognitive improvement, especially in working memory (WM) indices. This meta-analysis examined whether there is an advantage in training gains by comparing the results of two specific WM training approaches, Core Training (CRT) and Strategy Training (ST). Meta-analytic techniques were used to summarize 28 independent effect sizes from 24 studies with 1521 subjects, calculated only from studies that compared both training approaches in a single study. We found moderate effect sizes of trained tasks improvement with a clear advantage to ST over CRT, from which younger trainees benefitted the most. However, this advantage has almost disappeared for untrained tasks due to the limited improvement each approach produced on its own.