The word "teach" in Matthew 28:19, is from the Greek διδάσκω (didaskō), which means "to make a disciple." Obviously, we cannot "make" someone a disciple; we can merely present him with the information necessary to persuade him. In the case of making disciples for Christ, the Bible says that we are to preach the Gospel (Mk. 16:15; Acts 16:10; Rom. 1:15; 1 Cor. 1:17; etc.). The Gospel is declared in 1 Corinthians 15:1-4; it is the good news that Jesus died for our sins according to the Scriptures, He was buried, and He rose again, according to the Scriptures (also see Lk. 24:13-32). The Apostle Paul wrote: "For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek" (Rom. 1:16).
The Blue Letter Bible had this to say about the word "teach" in Matthew 28:20: it is translated from the Greek διδάσκω (didaskō), which means "to instruct as a teacher would a student." Teachers don't force people to become their students; students, in this case, born again believers hungry for God's Word and a greater knowledge of His will for their lives, voluntarily "sit under the teaching" of those gifted to teach them (1 Cor. 12:28; Eph. 4:11; etc.).
So, perhaps in the case of Matthew 28:19-20, we might consider the New American Standard Bible. It reads:
"Go therefore and make disciples of all the nations,
baptizing them in the name of the Father and the Son and the Holy Spirit,
teaching them to observe all that I commanded you;
and lo, I am with you always, even to the end of the age."