On Saturday, the Iranian team beat Brazil 3-1 (20-25, 25-20, 25-23, 25-20).
Iran had already defeated Egypt and Cuba in warm-up games in Tunisia.
Iran is pitted against the Czech Republic, Italy, Colombia and Bulgaria in Pool B.
Pool A consists of Tunisia, Brazil, Taiwan, Cuba and Belarus.
Japan, Egypt, Argentina, Mexico and German have been drawn in Pool C.
Russia, South Korea, USA, Nigerian and the Dominican Republic are in Pool D.
The 2019 FIVB Volleyball Boys' U-19 World Championship will be the sixteenth edition of the international volleyball tournament and the world championship for men's national teams under the age of 19, organized by the sport's world governing body, FIVB.
The tournament will be hosted by Tunisia in Tunis from August 21 to 30.