WASHINGTON (AP) — Employing videos that claim to teach toddlers, or flash cards for tots, may not be the best strategy. Simply talking to young babies in long sentences is key to building crucial language and vocabulary skills.

So says research into the troubling "word gap" that finds children from more affluent, professional families hear millions more words before they start school than poor kids. The lower-income students are left at an academic disadvantage that's difficult to overcome.

Stanford University psychology professor Anne Fernald says that gap starts to appear at around 18 months. That's younger than scientists once thought.

Research being presented at a meeting of the American Association for the Advancement of Science suggests what's essential is rich, varied language with good grammar that trains babies' brains to learn through context.

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