The cognitive load theory recommendations for enhancing the success of teaching are effective up to a certain boundary. The paper is dedicated to finding this boundary line in sentence length for 17-18-year-old students. The students filled in the blanks in 30 cloze tests. The cloze test results were correlated with the percentage of sentences over the boundary line. When the boundary-line was low, the coefficient of correlation increased with the rising of the line and the coefficient began to drop when the boundary line passed 140 characters. This size of the boundary line indicated the sentence length, up to which the taking of the load from the learners' mind was effective. The sentences with 130-50 characters were the most suitable for the students. (Contains 1 table.)