This episode's headline: Command Performance; Parents & Schools; College Costs; Summer Clouds. The guests include GEN. COLIN POWELL, Chairman, Joint Chiefs of Staff- Designate; SEN. JOHN WARNER, [R] Virginia; ADM. EUGENE CARROLL, [Ret.]; FRED HARGADON, Princeton University; RALPH NADER, Consumer Advocate; CORRESPONDENT: JOHN MERROW; ESSAYIST: ROGER ROSENBLATT. Byline: In New York: ROBERT MacNeil; In Washington: JAMES LEHRER