We found that multi-periodic low-mass stars discovered by Kepler K2 in the Upper Scorpius association are close binaries with typical separations of the order of 10 au and large mass ratios .
These stars were surveyed by speckle interferometry at the SOAR telescope with spatial resolution of 0 \farcs 04 .
Out of 129 observed targets , we resolved 70 pairs ( including 16 previously known ones and three new triple systems ) .
The distribution of projected separations of binaries with primary stars less massive than the Sun corresponds to a log-normal with median of 11.6 au and logarithmic dispersion of 0.60 dex , similar to M dwarfs in the field .
Future orbits of newly discovered binaries will provide accurate measurements of masses to calibrate pre-main sequence evolutionary tracks ; a tentative orbit of one previously known binary is determined here .