The scope of the current research is to figure out the relationship of cognitive failure, school engagement and school adjustment among second grade preparatory students, the research also studied the difference of high and low students in cognitive failure on school engagement and school adjustment. To achieve the research goal, the two researchers have built three psychological measures’ tools: Cognitive failure, School engagement and Academic adjustment. The pilot survey sample size of study was (120) students, the psychometric characteristics were calculated such as: validity, reliability, internal consistency and normal distribution. After verification of these characteristics, the three designed measures tools were applied to the final sample to test the current research hypotheses. The final sample of the research sample was (400) students in the second year. The results have shown that all dimensions and total score of cognitive failure were in average moderate level except attention errors factor was lower. Negative significant relation (Ρ≤ .01) between attention errors and authentic engagement was shown. Also, there is negative significant relation (Ρ≤ .05) between attention errors and school excellence factor. Positive significant relation (Ρ≤ .05) between behavioral engagement and academic perseverance in academic adjustment scale. No significance difference among high and low of cognitive failure on school engagement, and school adjustment except the significant difference (Ρ≤ .05) on relation with colleagues and teachers factor in favor of low in cognitive failure.