Jeanne S. Chall, an influential researcher who for decades was at the forefront of the debate over how people learn to read, died Saturday of heart failure at her Cambridge home. She was 78.

Chall, who retired as a professor of education emeritus in 1991, was one of the first psychologists to talk of reading as a learning process with developmental stages.

She started teaching at the Graduate School of Education in 1965 and in 1966 she established what is now the Harvard Literacy Lab, which trains instructors in how to teach reading.

Colleagues said one of Chall's chief contributions to her field was to urge reading teachers to give elementary school students the most challenging literature possible.

According to Mary E. Curtis, who directs the Center for Special Education at Lesley College, Chall would push teachers to give students books that were beyond their reading level, in order to further their knowledge.

Chall also helped shape one of the most heated arguments in elementary education. Educators have argued for decades about whether children should first learn to generally understand texts that they read or if they should concentrate on phonics, or sounding out words one by one.

Chall weighed in on the discussion in 1967 in her first book, Learning To Read: The Great Debate (1967).

The book compiled evidence from over 100 studies. Her colleagues said it has framed the debate ever since.