The principals’ monitoring of instructional practices is necessary and important to enhance teaching and learning processes and outcome in schools. Accordingly, the Teachers Service Commission developed the performance appraisal as a monitoring tool for improving teaching and learning processes and the outcome in public schools. Despite this measure being in place, teaching and learning outcome has remained consistently low, especially in Kajiado County. The objectives of the study are to: assess the influence of principals’ monitoring of teacher preparation of professional documents on teaching and learning outcome and determine the influence of the principals monitoring of teachers instructional delivery on teaching and learning outcome. The study employed a descriptive survey design. This study population of study comprised 727 respondents in all the 9 public secondary schools in Kajiado. These respondents included 122 teachers, 594 students and 9 principals. Out of these, 342 respondents were sampled and they were comprised of 9 principals, 97 teachers and 201 students. Proportionate sampling was used to draw a sample of 97 teachers’ and 201 students per school. Further, simple random sampling was used to sample teachers while convenience sampling was applied to draw the sample of students to participate in the study per school. Data was collected by questionnaires and interview schedule. A pilot study was conducted in two schools for the purpose of addressing validity and reliability of the instruments before the actual study was conducted. The analysis of quantitative data was done using frequencies, percentages and means and then presented in tables, figures. Qualitative data was arranged into themes and presented through narration and in verbatim. The study established that principals’ monitoring of teachers’ preparation of professional documents has significant influence on teaching and learning outcome. It revealed that principals' monitoring of teachers’ instructional delivery significantly influenced teaching and learning outcome.