Was there class mobility during the middle ages?

1st AnswerThere was limited class mobility during the Middle Ages. People did move from one class to another, but aside from serfs being liberated from their bondage to the land, it did not happen often. Serfs could be freed by running off the manor, and if they did not return within a year, they were regarded as free, effectively putting them into the middle class.

The Church provided another avenue for advancement, as a bright young man could be educated by the Church, become a priest, and advance to being a bishop or even a pope. For example, Pope Leo III, who crowned Charlemagne as emperor, was the son of a farmer. Such advancement meant that other members of the family could profit from any connections that were formed.

Upward mobility could also be achieved in other ways, such as through connections with members of the nobility. An Excellent example of this is the case of Owen Tudor, who was a Welsh commoner with some connections to Welsh nobility. He was an educated man who took a position as the steward for the widow of King Henry V of England after she was widowed. They married, which was technically illegal, but they got away with it, and they had several children. The children were half siblings of King Henry VI, and so two of them were elevated to the nobility. One of these, Edmund Tudor, 1st Earl of Richmond, had a son, Henry Tudor, who became King Henry VII of England in a compromise at the end of the War of the Roses. So the family went from commoners to nobility in one generation, and from nobility to royalty in the next.

There are links below to articles on Owen Tudor and the Tudor Dynasty.

2nd AnswerPerhaps, but not very common, if you joined the clergy as a priest or friar than essientially you can be moved up from a peasant or merchants, also some merchants and peasants joined the military and some time were able to own land or manors, it can possibly work the opposite as well, someone could be banished from court or excommunicated from the church which would move them down in rank, a woman can marry into a higher class, and could also marry into a lower class but was rare because women came with a dowery (money, estate, etc.,) from there father and would rarely be approved to marry below class, and a man could not marry into a higher class, but like I said, its all rare, and commonly doesn't happen