In this research study three subject didactical measuring instruments were compared with regard to certain psychometric characteristics of a group of grade nine learners in the Tzaneen and Phalaborwa region, in the Northern Province. The primary goal of this study was to optimize learning competencies with regard to subject context. The SOM-, LEMOSS(II)- and LCH-questionnaires can be applied at the start or at the end of an academic year to an individual or to a group in order to identify learners who need specific help, counseling, remediation and support in the subjects mathematics, natural and domestic sciences in order to facilitate learning. The following aspects have been handled in this study, such as: In chapter 1 an attempt is made to clarify and define the title and certain relevant concepts. The research statement and questions are formulated. The research design is briefly discussed and the primary goal and objectives are set. Other aspects that enjoy attention include the types of research that were used, the method of sampling, data gathering and analysis, as well as the progress of the study. Literature on subject didactics is discussed in chapter 2 for the conceptualising of basic related aspects by means of a macro-model for the optimising of learning competencies in the context of a specific subject. This model emphasises subject content, form and competencies that should be taken into consideration when planning a learning opportunity. Other aspects concerning learning, namely relevant theories, approaches, models, styles, strategies and motives were discussed in order to facilitate learning in mathematics, natural and domestic sciences. In chapter 3 the SOM-, LEMOSS(II)- and LCH-questionnaires as diagnostic instruments are described. The diagnostic value, background, categories and psychometric aspects of the measuring instruments are briefly discussed. In chapter 4 the method of investigation used for the comparison of the SOM- LEMOSS(II)- and LCH-instruments regarding their reliability and validity is described and it includes the goal, hypothesis and method of sampling as an extension of the research design. The way in which descriptive and inferential statistics are conveyed is theoretically described In chapter 5 the results and qualitative conclusions of the empiric-analytical investigation are included. The SOM-, LEMOSS(II)- and LCH-questionnaires are compared with regard to reliability and validity of a group grade nine learners in the Tzaneen and Phalaborwa region. Reliability is discussed by means of test-retest reliability and pared observations. Pared observations include staggering, locality and pared t- and sign-rank testing. Validity refers to criteria referenced validity with regards to simultaneous and predictable validity. Simultaneous validity is described by means of the relation between the subject mark and the field, and by stepwise and multiple regression analysis. In chapter 6 the study is concluded with the brief answering of the research questions and by describing the research findings by means of the research statement. Possible limitations are shown and recommendations for future research are made.