This study examined teachers’ frequency of preparation and use of lesson plans. The study location was Igunga District of Tabora Region in Tanzania. Mixed approach and explanatory research design were used and a total of 69 respondents were sampled. Among them, 60 were teachers from four purposely selected primary schools, four were head teachers and five were school quality assurance officers. Data was collected through a questionnaire, an interview schedule and document. Analysis of data was done through the thematic approach and the descriptive statistics. The established that not all teachers prepared the lesson plans; there were those who prepared frequently, those who prepared occasionally and those who did not prepare at all.  It is also concluded that not all teachers used the prepared lesson plans in the classrooms during teaching and learning process. There were those who used lesson plans frequently, those who used lesson plans occasionally and those who did not use the lesson plans at all in the teaching and learning process. The researchers therefore recommended that teachers should be given more in service training on the preparation of lesson plans and they should be closely capacitated for them to refrain from teaching without prerequisite guiding documents including lesson plans. Head teachers as internal quality assurers and the DSQAOs as external quality assurers should closely supervise teachers to fulfill this crucial role as professional teachers.  Educational leaders at district and national levels should ensure effective preparation and use of lesson plans to teachers through close monitoring and facilitating teachers with all necessary tools for the preparation of lesson plans.