xsl:variable

Can someone tell me why the following doesn't work?

<xsl:template name="myTemplate">
 <xsl:variable name="sizePresent" select="'no'"/>
 <xsl:for-each select="attribute">
  <xsl:if test="@type='Size'">
   <xsl:variable name="sizePresent" select="'yes'"/>
   Size is present.
  </xsl:if>
 </xsl:for-each>

 <xsl:if test="$sizePresent='no'">
  Size was never found.
 </xsl:if>
</xsl:template>

When I run it I get:
Size is present.
Size is present.
Size is present.
Size was never found.

What I want is either:
Size is present.
Size is present.
Size is present.

or:
Size was never found.

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list