The Diocesan Sunday School is affiliated to the Mar Thoma Sunday School Samajam headquartered in Thiruvalla, Kerala, India. The Diocesan Sunday School is divided into eight regions and then into centers. Diocesan Bishop is Rev. Larry Varghese Mar Theodosius gives great leadership for the Sunday school. Rev. Mathew George is the Sunday School Vice-President.

There are 56 Sunday Schools consisting of over 4000 students and 660 teachers. The Sunday schools in this Diocese follows a curriculum developed by this diocese. Classes are conducted from Nursery to Teachers Training. The Diocesan examination is conducted in the month of the May and students from 5th Grade through 10th Grade participate in this examination. Plaques and certificates are given for those who attain good grades in this examination. The Zones and Regions conducts Conferences, teacher retreats and camps for the fellowship of the teachers and students. The Regions also conduct Regional competitions in Singing, Elocution and Bible quiz. The students also participate in various fund raising activities for charity and support some missions in India. The VBS is another activity of the Sunday school during summer and the Diocesan Sunday school decides on the VBS curriculum.
As the Christian Education Department of the Mar Thoma Church, the Sunday schools play an important role for the children in accepting Jesus Christ as their Savior and to grow in Christian fellowship and worship life.
Office bearers (2017-2020) are: Rev. Larry Varghese : Vice-President, Mr. Reji Alexander : Secretary, , Mr. Thomas Easo Treasurer, Mr. George P. Babu: Assembly Representative. 

MAR THOMA SUNDAY SCHOOL SAMAJAM
The reformers realized the importance of Bible Study, as essential for spiritual renewal and growth. The opening of Sunday Schools thus became a natural development in the way of Christian nurture. The formal inauguration of the Sunday School Samajam comprising all the Sunday Schools which had already been started in the parishes took place at Maramon Convention in 1905. Mr. V.P. Mammen (Later, Vicar General V. P. Mammen Kasseessa) was elected as the General Secretary. The growth and development of the Sunday School Samajam as one of the leading Christian Education organizations in India was the result of the extraordinary organizing ability of Rev. V. P. Mammen and his untiring efforts during a period of 47 years. In those days, though with limited travel facilities he visited churches in different places,traveling in bullock carts and riding bicycles. He organized syllabuses for the different grades and published the lessons to be taught in various classes. A publication entitled Sandarsini began to be published in 1911 containing articles helpful to the students, teachers and parents and lesson notes for Sunday School teachers. Since 1952 text books are published for the various classes. From 1977 the curriculum of the Christian Education Council of India is followed by the Sunday School Samajam. 

Rev. Dr.K. K. George joined the work of the Sunday School Samajam in 1952 and was General Secretary of the Samajam from 1952 up to June 1982, after the demise of very Rev. V. P.Mammen. Both of them labored in this great cause dedicating their extraordinary powers of head and heart to the cause of Christian Education of children. Classes are arranged for a period of 15 years from the age of 5, so that by the time the Sunday School course is completed, the students will have sound knowledge of the scriptures and the doctrines of the Church. 
Sunday Schools are arranged in every parish. In larger parishes there will be two or more Sunday Schools according to the need. 
Inspectors are allotted to supervise the work of the Sunday Schools in a given area, and organizers are appointed in each Diocese. Examinations are held every year, arranged from the Central Office and competitions are held at the Diocesan and Central levels. 
The Sunday School Samajam celebrated the Platinum jubilee in 1980. The Christian Education Center was established at Charal Mount, Kuriannor in 1972, providing one of the most attractive camp sights for children and for the training of teachers. The High School at Edakulam and the boarding house attached to it are run by the Sunday School Samajam. 
Vacation Bible School Vacation Bible Schools (V. B. S.) have been started as a project of the Platinum Jubilee celebrations. The classes extend for a period of ten days during summer holidays. The syllabus is carefully prepared. The children look forward to these classes where they get opportunity for learning new songs and for participating in work projects. The children are led to accept Jesus Christ as their Lord and Savior. 
Rev. Ninu Chandy directs the work of the Sunday School Samajam as General Secretary at present. 
There are 945 Sunday Schools and 137263 students.