The study examined the extent to which secondary school teachers ensure the validity of the tests in accordance with the 2021 NECTA guidelines in Ukerewe District -Tanzania. The researcher adopted Validity theory to guide the study. A parallel convergent design under mixed methods research approach was used. The probability and probability sampling technique was used to obtain 56 respondents from 479 populations. The categories of the sample involved 6 public secondary schools, 6 Head of Schools, 42 teachers, 1 Chief District School Quality Assurer and 1 District Secondary Education Officer. For data collection, the study utilized a questionnaire and interview guide. To ensure the validity of the data collection tools, research experts from MWECAU validated them. The reliability of the questionnaire, specifically for the Likert scale items, was estimated using the Cronbach Alpha technique, yielding a coefficient of 0.768. The trustworthiness of the qualitative data was maintained through the use of triangulation of instruments and peer debriefing. Quantitative data were analyzed using descriptive statistics, while qualitative data were coded, analyzed thematically, and presented through direct quotations. The study found that public secondary school teachers are alert of the important aspects of valid and quality test construction as stipulated by the 2021 NECTA guidelines. Also, the study concludes that 2021 NECTA guidelines are moderately practiced by secondary school teachers in ensuring the validity of tests in school-based continuous assessment practices. But they are negatively affected by a lack of proper understanding and require skills in linking the practices with competency-based outcomes. The study recommends that the NECTA organize and mobilize in-service training for public secondary school teachers, heads of schools, District Secondary Education Officers, and District Quality Assurance Officers on implementing and using the 2021 NECTA guidelines for continuous assessment in secondary schools.