There were three purposes of this study: 1) to construct Thai word spelling writing exercises for developing Prathom Suksa four students? word spelling writing ability, including finding  the efficiency of the exercises to meet the standard criterion of 80/80, 2) to compare student?s achievement before and after the implementation of the exercises, and 3) to find out the student?s satisfaction towards the exercises.
The sample in this study consisted of thirty students, studying in the second semester of 2009 academic year, in Wat Bangwua (Saisermwit) School, Bangprakong, Chachoengsao. The instruments used in the experiment were six Thai word spelling writing exercises, developed by the researcher, two  parallel achievement tests used for pre-test and post-test, and the questionnaire to survey the students? satisfaction toward the exercises. The statistical devices employed for the data analysis were mean, percentage, standard deviation and t-test dependent, to examine the efficiency of the exercises and to find out the differences of the achievement test scores before and after using the developed exercises.
The findings of the study were as follows :
1.  The efficiency of the Thai word spelling writing exercises was found  to be 87.17/83.44  which were higher than the 80/80  per cent  setting  standard criterion.
2.  Students? learning  achievement  after  using t he  exercises  was  statistically  significant  higher  than  before  using  the  exercises  at .01 .
3.  Students? satisfaction towards the exercises is at the highest level.
