Testing of the influence of starspots on the derived masses and ages of pre-MS stars. Left: H-R diagram including stars from the Upper Sco association. Also plotted are 5 Myr isochrones for four different starspot covering fractions, from 0.00 to 0.85. Center: the masses and ages derived for each Upper Sco star from models with different starspot fractions. The yellow and cyan circles reflect the average age above and below 0.9 M_⊙. Right: the average age of the higher and lower-mass ranges for every f_spot value in the SPOTS models. At f_spot = 0, the higher-mass stars have older measured ages. As f_spot increases, the average derived ages increase both for higher and lower masses, but the lower-mass average overtakes and surpasses the higher-mass average. The numbers above each pair of points is the average derived mass of all Upper Sco stars, demonstrating that this metric also increases with increasing f_spot.