The report indicates that 85% of participants used Instagram at least once a month compared with an equivalent figure of 84% for Snapchat.
But rankings were reversed when the teens were asked which they preferred.
Snapchat was picked as the "favourite social platform" by 46% of those questioned, while Instagram was chosen by 32%.
That figure may offer some reassurance to Evan Spiegel and other chiefs at parent firm Snap that their efforts to address a backlash against an unpopular redesign are working.
But it is the engagement figure that has dominated headlines, and threatens to feed a narrative that Snapchat is on the decline. For full story click here.