In parochial schools and Catholic hospitals of the past (and often of the present), a crucifix might hang in each room. It's a good idea to set your room up with sacramentals, both displayed and available to use. A crucifix or a statue of a saint or the Blessed Virgin Mary can keep hearts turned to God during the school day. A holy water font can be placed in the doorway and refilled after each Sunday Mass. Rosaries should be as easily at hand as pencils and rulers. Icons of saints can be set in niches. Candles (managed safely if little kids are present) can be lit in prayer or during moments of recollection.
Don't spare your shelves the burden of good books. It's enriching to have several translations of the Bible available, as well as lives of the saints in narratives with varying degrees of depth. The catechism should be on hand, and copies of older catechisms (such as "The Baltimore Catechism") can be nice to have. Readings from the Church fathers and doctors of the Church (like Teresa of Avila, John of the Cross or Augustine) are helpful in forming children's faith as they grow.
The Church divides the year into seasons of Easter, Christmas, Advent, Lent and Ordinary Time. Attending to these seasons at home lends a pleasant rhythm and helpful structure to the school year. Holy Days of Obligation and feast days for saints can be occasions for special activities or meals or rest from burdensome tasks. The phrase "red letter days" comes from a time when feast days and holy days were marked in color on calendars, and the spirit of anticipation and celebration the phrase awakens in us can be revived in our home schoolroom. Make and hang Stations of the Cross during Lent; hang an Advent wreath with purple, rose, and white candles for Advent; decorate with purple cloth for both.
Two thousand years of culture have made an incredible number of works of art available for our use as Catholic home schooling parents. Display copies or photos of works by El Greco, Michelangelo, da Vinci or Huberto Maestas in your classroom. Learn about historical periods by displaying pictures or models of basilicas, cathedrals, grottos, buttresses and stained-glass windows.
In his Canticle of Creation, St. Francis prays, "Praised be my Lord God with all his creatures, and specially our brother the sun, who brings us the day and who brings us the light; fair is he and shines with a very great splendor: O Lord, he signifies to us thee!" Remember that all creation can be brought to our remembrance Ad Majorem Dei Gloriam (For the Greater Glory of God), and fill your room with spurs to your children's curiosity and creativity. Photographs, diagrams, models and maps illustrating the science and the history that you are studying, intricately worked equations, or literary quotes and passages can beautify the classroom walls and shelves. Try to include family photographs or genealogy trees to connect your children with the family, which holds a special place in the life of the Church, and with any Catholic traditions that may have been passed down through it.