The purpose of this investigation was to study the effectiveness dimension of educational leadership of elementary school principals in the Houston Independent School District. Reddin's "3-D Theory of Leadership Effectiveness" served as the theoretical basis for the investigation. Effective leadership is a function of a leader's ability to match appropriately one of the four basic styles to a situation demanding such a style. Each of the four basic styles (separated, dedicated, related, and integrated) have a less effective and more effective counterpart depending on its appropriate or inappropriate application to the situation. The identification of the principals' dominant styles and the relationship of these dominant styles to the selection of decision alternatives, as well as to the effectiveness of principals in selecting appropriate decision alternatives comprised the first five hypotheses. Hypothesis six examined whether principals with nondominant styles were more effective than principals with dominant styles, while hypothesis seven investigated if years of experience enabled principals to be more effective in selecting the appropriate situation. Research Procedures. The effectiveness of the elementary school principals was assessed by use of W. J. Reddin's and M. K. Reddin's "Educational Administrative Style Diagnosis Test--Modified" (EASDT-M) and the "Elementary Principals' Administrative Style Questionnaire" (EPASQ), which was of original design. The EPASQ consisted of twelve hypothetical situations reflecting four administrative areas which confront elementary school principals: instruction and curriculum development, staff personnel, pupil personnel, and schoolcommunity relations. Each of the four basic styles were demanded in three different situations and each situation also consisted of four possible choices reflecting each of the basic styles. Out of a possible 168 participants in the Houston Independent School District, 114 (68%) elementary school principals submitted data from which analysis, interpretations, and conclusions were derived. The chi square (X2) statistic was utilized at the alpha .05 level of significance to test all seven hypotheses. Findings and Conclusions. Contrary to what was hypothesized, significant relationships were not found between the principals' respective dominant styles and their ability to select the appropriate response demanded by each of the twelve situations. Principals with nondominant styles did not demonstrate more flexibility in applying appropriate styles. In addition, years of experience did not necessarily enable principals to be more effective in selecting the appropriate situations as measured by the EPASQ. A principal finding was that principals refused to abandon their high task and high relationships orientation even when the situations on the EPASQ did not require such behavior. Principals selected the separated (25%) style as the highest single dominant style on the EASDT-M and selected the integrated (77Z) style as the highest single dominant style on the EPASQ. Recommendations. It is recommended that continued research be carried out in order to determine the reliability and validity of both the EASDT-M and the EPASQ. Additional data needs to be collected by conducting subsequent "on-site" case studies in order to determine if respondents' answers to the simulated situations are also reflected in their actions as they fulfill their daily administrative responsibilities. It is also recommended that the feasibility of using such instruments as the EASDT-M and the EPASQ or similar instruments by universities and school districts as diagnostic tools in order to improve leadership among all level administrators be examined. Finally, it is recommended that only one instrument be utilized which will accomplish the identification of the leader's style and the appropriate flexibility of style as it relates to the situation.