Purpose: The present study aimed at developing and validating a self-development training package and determining self-development's effectiveness on job variables and human capital agility among secondary school principals in Isfahan. Design/methodology/approach: In the first phase, the researcher conceived a full version of the self-development training package by studying the theoretical evidence of research and interviewing experts as well as using content analysis. The questionnaire was presented to several experts (n = 8) in that field of study for evaluation after compiling the initial version of the self-development training package, with the aim of determining the face and content validity. In the second phase of the study, the effectiveness of the self-development training package was experimented on secondary school principals using a quasi-experimental pre-test-post-test design and follow-up with a control group. Findings: The evaluation results were suitable for the training package based on the proposed Lawshe method. The results also indicated that the implementation of a self-development training package in the experimental group had a significant effect on job performance and its dimensions, as well as human capital agility. The effect of the training package on increasing job performance in the post-test stage was 55.3% and was 50.2% in the follow-up stage. Also, the effect of this package on increasing the agility of human capital in the post-test phase was equal to 34.8% and was equal to 28.9% in the follow-up stage. Originality/value: Question 1: What are the components of a self-development training package? Question 2: What is the credibility of the developed training package from the experts' point of view? Question 3: Does the self-development training package have an effect on job performance and its dimensions? Question 4: Does the self-development training package have an effect on human capital agility?.