This January, 14-year-old Francis Tiafoe beat William Blumberg 6-0, 6-2, in an All-American boys’ singles final at Les Petits As in Tarbes, France. Alicia Black, a 13-year-old who trains full-time at the USTA Training Center Headquarters in Boca Raton, Fla., reached the girls’ singles final where she lost to Jacqueline Cristian of Romania, 6-2, 6-3.