WASHINGTON — The President John F. Kennedy students learn about today is not their grandparents’ J.F.K.

In a high school textbook written by John M. Blum in 1968, Kennedy was a tragic hero, cut down too soon in a transformative presidency, who in his mere 1,000 days in office “revived the idea of America as a young, questing, progressive land, facing the future with confidence and hope.”

By the mid-’80s, that heady excitement was a distant memory, and Kennedy a diminished one. A textbook written in 1987 by James A. Henretta and several colleagues complained of gauzy “mythologizing” about his tenure and said the high hopes he generated produced only “rather meager legislative accomplishments.”

The first — and for many the last — in-depth lesson that American students learn about the 35th president comes from high school textbooks. And on the eve of the anniversary of his assassination 50 years ago, a review of more than two dozen written since then shows that the portrayal of him has fallen sharply over the years.

In general, the picture has evolved from a charismatic young president who inspired youths around the world to a deeply flawed one whose oratory outstripped his accomplishments. Averting war in the Cuban missile crisis got less attention and respect. Legislative setbacks and a deepening commitment in Vietnam got more. The Kennedy-era glamour seemed more image than reality....