Noticing relationships between similar things and developing rules for treating things the same or differently, based on characteristics like color, size, shape, and texture provides the basis of beginning mathematics learning. Based on the view that teachers and parents of young children should provide children with age-appropriate words, materials, and experiences so they can investigate math concepts with adult support and encouragement, this booklet with accompanying videotape describes the 13 math-related key experiences of the High/Scope model grouped under classification, seriation, and number. The booklet provides lists of materials that promote math exploration and descriptions of teaching strategies that will help adults recognize and make the most of math opportunities throughout the day. Included in the booklet are pictures and anecdotal examples of children participating in the math-related key experiences. The booklet concludes with a list of materials and a strategies checklist. Each of the 13 key experiences are introduced in the accompanying 60-minute videotape, illustrated with sequences of children and teachers in a variety of High/Scope classrooms. The second part of the videotape shows four extended video scenes from High/Scope classrooms, presented without narration as in-depth examples of how the math-related key experiences naturally unfold; adults are shown responding to children's play ideas and following children's cues and interests as they help them carry out and develop their ideas. A viewer guide to the video describes the components of the video; provides a strategies checklist for classification, seriation, and number key experiences; and lists five additional resources from High/Scope. (KB)