Complex sentence: Ungraded system was not included, because the principle of variation of time did not fit the scheme, because, according to the interpretation of the committee, equality demanded the duration of secondary schooling had to be of equal length to all.
Split into simpler sentences: Ungraded system was not included, because the principle of variation of time did not fit the scheme. That was because, according to the interpretation of the committee, equality demanded schooling to be of equal length to all.